Method of making sound films



y 2, 1940- E. GERLACH 4 METHOD OF MAKING SOUND FILMS I Filed Oct. 19, 1927 2 sheets-sheet 1 jnt enfo'rx 0% Way J 'rLQZS.

Filed 001:. 19, 1927 2 sheets-sheet 2 INVENTOR E. GERLA CH I "I V 2 mm ICROPHONE ATTORNEY Patented July 1940 p r 2,266,547

UNITED STATES PATENT OFFICE METHOD O lf/MAKING SOUND FILMS Erwin Gerlacli, Berlin-Siemensstadt, Germany,

assignor to Siemens Jr Halske Aktiengeleilschait, Siemensstadt,'near Berlin, Gel-mini, a corporation of Germany i Application ocicbci- 19, m1, serial no. 221,201

1 In Germany April 9, 1927 so claims. f (01; nil-100.3

This invention relates to a method of making sium- The iginal or neg ve record will then sound films by which undesired noises produced be clear except in the area near the lines through during the reproduction oi the sound are ret general p s f the sound urv A r pr duced or lim t d, duction or positive sound record may then be 5 In the optical reproduction of sound records, produced by printing from the modified Original. I

. undesired noises are produced, which become Th s reproduction sound record will be fully exnoticeable when the amplitude of the reproposed except in the area bounded by e es duced sound is small. A considerable portion of through the gener l epiees f the sound curve. this undesired noise is due to defects in the sound In another method, a mask or lormer'is made record being reproduced, such as scratches, dots from d a i or positive py of t o al 1 or irregularities in t photographic ]9,yer D sound record. The mask or former is blackened fects which are located on a blackened surface throughout the area defined y t e es t ou h of the reproduced record, or covered by a shutthe ap e' of the Sound curve, d hes a clear ter, will not produce any undesired noise. Thus, are c rresponding to the clear area of a readif the reproduced record is at all times as dark negative Positive py of the Original ound as possible, the undesired noise will be a minio The mask or former ay. o instance. mum. For example, if the amplitude or the rebe hand-made by coating a ne ative or positive corded sound is small-or equals zero, as in silent py of the original Sound rd Wi h n Opaque scenes, the corresponding portions of the repro- Substance Within the area bounded y the lines so duced record should be substantially completely hrough the aplces oi the sound curve and reblackened, moving the exposure on the remainder of the The object of the present invention is to re- A reproduction positive py is then duce the light energy impressed on the scanning pr e in the usual manner from the original device to the minimum value which. will carry o negative sound record- Before development,

the modulation required for the sound being the mask or former is superpose on he exposed 28 reproduced, reproduction or positive copy and a second ex- In accordance with the present invention, the p e madei second e posu e ;will only undesired noises are reduced or eliminated by afleet the.lllii'nil-losedv areas of the eproduction blocking or shuttering oil ,the light passing or positive'fllm lying outside thearea 'deflned so through the blank portions of the reproduced by h sk r f rmer- The reproduction or 80 sound record, particularly at the points where positive py i then developedthe sound record is of relatively small ampli- In ordinary Sound films. h m n permeabiltude. This result may be achieved by several ity to light s p ac ca t e ame atall portions methods. For instance. the reproduced sound f the though the insta taneous permearecord may be blackened in the partially exposed bility n l y V e ve and below this mean 35 or unexposed portions until the light transmitted p r li S a u t, an u desired noise through the film is reduced to the extent indiis p o ced i e r p uctio of the sound cated above. If the reproduced .record is one record, which becomes very perceptible t h se m de by th an d variabl ar a th d portions which correspond to recorded sounds of 40 in which the record track is completely blackrelatively Small intensity- It Will be pp e ened within an area. bound d by th line that, in a film made in accordance with this through the general apices of the sound curve, v n h m an permeability to li h is the additional blackening may be obtained by sma e at p s o t e record co respondin covering the unexposed portion of the reproto sounds of relatively small intensity than at I duced film with an opaque substance almost up por i ns r pon o o n s of relatively g to the line through the general apices of th great intensity, although successive portions of sound curve, that is, mainly at the points of relthe record vary in their instantaneous permeaatively small amplitudes. bility to light in accordance with the amplitude Another method consists in removing from the of the sound recorded.

original or negative sound record the blacken- As the mean permeability to light of the re- 0 ing due to the exposure during recording almost production or positive sound record is less than up to the lines through the general apices of usual; particularly at the portions of the record the sound curve. The exposure may be removed corresponding to sounds of relatively small inin many well-known manners, such as by the tensity, the mean permeability to light of the useof photographic reducers containing potasoriginal or negative sound record must be greater 5 than usual. that is, the exposure 01' the'original or negative sound record must be reduced. In a further method in accordance with this invention, the original or negative 'film is shuttered during recording to reduce the light impressed on the film to the minimum which will carry the modulation due to the sound. In records made by the so-called "variable area method, the shuttering may be effected to such an extent that it reaches completely or almost up to the lines through the general apices of the sound curve. This shuttering should not be carried out too-quickly, in order to prevent the production of spurious sounds or noises from subsequently being produced by the loudspeaker.

In cases where it is desired to avoid any change in an existing reproduction or positive sound record. the quantity of light transmitted through the reproduction or positive record may be controlled during reproduction by an. auxiliary shutter interposed in the reproducing light ray. This auxiliary shutter may be operated manually or controlled automatically in accordance with the amplitude of the sound record curve. The control by this auxiliary shutter of the quantity of light transmitted through the film will supplement the control exercised by the regular reproducing system comprising the light source, the light sensitive cell, and the reproducing system.

In the drawings:

Fig. 1 shows in plan view a portion of an ordinary negative sound film; I

Fig, 2 is a similar view of a portion of a positive sound film embodying the invention;

Figs. 3, 4 and 5 are views showing how a negative sound film, Fig. 3, is modified according to the invention into the form shown in Fig. 4 from which the. improved positive film Fig. 5 is then obtained;

Figs. 6, '7 and 8 are views showing how a negative or positive sound film, Fig. 6, is modified according to the invention to produce the mask or former shown in Fig. 7 by which the improved positive film 8 may be obtained;

Fig. 9 is a diagrammatic view of an apparatus for reproducing sound in accordance with the invention;

Fig. 10 is a detail of a shutter used in the apparatus shown in Figs. 9 and 11; and

Fig. 11 is a diagrammatic view of an apparatus for recording sound in accordance with the invention.

Fig. 1 shows a portion of the length of a film sound record produced by the so-called "variable area method of sound recording, The curve aib, varying in accordance with the recorded sound, forms a line of demarkation between the transparent portion a, c, d, b, and the blackened portion a, e, .f, b of the film c, e, f, d.

In Fig. 2 is shown a film of the same character as the film shown in Fig. l, but with the novel additional blackening in the formerly transparent portion a, c, d, b whose boundary line a, h. reaches almost up to the dotted line through the apices of the sound curve. Thus, only the narrow slip a, b, a, h and the spaces between the recordedwaves are transparent. Thus any defects which are present in the area 0. a, h, d are blackened out and the noise produced during reproduction will be scarcely noticeable. It will be noted that the mean permeability to light of the-film shown in Fig. 2 is much less when the recorded sound is of relatively small amplitude tive film sound record of the character customarily produced by the so-called "variable area method of recording and having the usual blackened or opaque lower portion. A suitable photographic reducer, such as a potassium reducer, is applied to the blackened area of the record and reduces the silver deposit thus making the record transparent. The result of this reduction is shown in Fig. 4, in which the blackening has been removed from all portions of the record except the'area bounded by the lines through the apices of the sound curve. The modified negative shown in Fig. 4 is then copied photographically to produce the positive or reproduction record shown in Fig. 5, in which the entire width of the record is blackened except the area bounded by the lines through the apices of the sound curve.

Fig. 6 shows a portion of the length of a positive film sound record of the character produced by the so-called "variable area" method of recording, having the curve a, b varying in accordance with the recorded sound and forming a line of demarkation between the transparent and the exposed portions of the record. The sound record is contained within the area bounded by the lines through the general apices of the sound curve, as indicated by the dotted line u. A positive copy of the record, shown in Fig. 6, is treated to render the area between the lines through the general apices of the sound curve (the area between the dotted lines 11. in Fig. 6) completely opaque, which may be done, for instance, by completely exposing this area to light or by coating this area with an opaque substance. The modified copy is shown in Fig. 7 in which the completely opaque area is indicated at S, The

exposure in the lower portion of the record indicated by the single lines of hatching may be removed if desired by any known' photographic reducer. After the exposure is reduced, a mask or former is produced in which the area between the lines through the general apices of the sound curve is opaque, and the remainder of the area is transparent. A positive copy is made 01! the negative record, as shown in Fig, 6, by the usual photographic processes. Before this copy is developed, the former or mask shown in Fig. 7 is superposed on the exposed positive copy and a second exposure to light is made. The positive copy is then developed. As shown in Fig. 8 by the hatching lines sloping similarly to the lines in Fig. 6, the first exposure produced a latent image in the area a, e, I, b. The second exposure will notafiect the area between the smooth lines 1', k, h, g which is covered by the opaque portion S of the mask or former shown in Fig. 7, but will affect and cause'a blackening oi the area 0, d, h, g. Also, if the blackening in the lower portion of Fig. 7 has been removed by a reducer. then the second exposure will re-expose the area i, e, f, k. This second exposure is represented in Fig. 8 by the hatching lines sloping in the 6 opposite sense to the hatching lines in Fig. 6.

The developed film as shown in Fig. 8 is com.- pletely blackenedexcept in the area g, h, b, a, bounded by the lines through the apices of the sound curve.

Fig. 9 is a diagrammatic view of a sound reproducing system in which the non-exposed portions of the sound record are covered during the process oi reproduction. so that a modification oi the reproduced film is not required. Light ano es? the light-in theusual manner. The light modulated by its passage through the sound film o is focussed by a second lens system on the light sensitive cell Z. The output of the light sensitive cell Z may be supplied in the-known manner to a sound reproduoer-or loudspeaker. In: terposed in the beam of light from the source 1 is a shutter m, n composed of afixed part m and a movable part 1: fastened to an armature pivoted at q. The armature is controlled by the current fiowingin an electromagnet 1'. Light from a suitable source t is focussed by a lens system on the moving film o, andafter modulation by the film o is focussed on a light sensitive cell 11.. The output of the light sensitive cell 1:, suitably amplified if desired, is supplied to the electromagnet r and controls the movement of the shutter n. The shutter n is desi'gned so as to limit the light energy-impressed by the source I on the film o to an, amount which wm be substantially completely modulated by the film '0, that is. the transparent portion of the film will be shuttered up completely or almost up to the line through the apices of the sound curve. The amount of the record which is shuttered ofi will depend on the output current of the light sensitive device 9, and, as the device 11 is excited by. 4 light modulated by the film 0, will depend on the amplitude of the waves recorded on the film 0.

In order to insure that the shutter n will move only in conformity with the characteristic of the line through the general apices of the sound curve and not with the variations of the indi vidual frequencies, one or more choke coils u may be inserted in the circuit between 1: and r, and in some cases associated with parallel or shunt condensers u so as to prevent oscillations of the frequency of the sound from operating the electromagnet r. V

The choke coils u may be omitted if the light ray from the auxiliary light source t is made sufficiently wide, lengthwise of the film o, as to be larger than or a multiple of the distance lengthwise oi' the film o occupied by one complete cycle of the lowest frequency which can be recorded. Thus, in this case, it is not the amplitude of an individual frequency which acts on the shutter, but rather the mean or average amplitude of the 'sound record in the area covered by the light ray.

The distance along the film between the point scanned by the main optical system l-n and the point scanned by the auxiliary optical system t-p is so chosen that the time required for the film to move along this path is of the order of the time of reaction of the auxiliary system from the instant that the light ray is modulated until the shutter part n is put in motion. This time of reaction is substantially dependent on the inertia of the cell p, the dimensions of the chokes v and the dimensions of the magnet winding r.

Fig. shows a shutter m, n of well known type which permits of shuttering the film in a direction transverse of the film. The two active edges of the shutter parts maybe arranged to form an acute angle with each other, so that the degree of the shuttering effect transverse of the film will be a multiple or sub-multiple of the movement in the direction of the arrow of the shutter part n. The auxiliary device incorporated in Fig. 9, can, in the somewhat modified condition shown in Fig. 11, also be incorporated in a film sound recording system. In this case, it is necessary to substitute for the photoelectric cell 11, an auxiliary a microphone or a circuit from a microphone such as M1, connected to the auxiliary circuit comprising the choke coil 22, shunt condenser is and the magnet r controlling the shutter m, n. The shutter m, 1| is arranged to cover substantially all of the portion of the film 0 which will be exposed by the well known "variable area" recording apparatus R controlled by the microphone M1, substantially up to the line through the apicesor the sound waves, thus producing 'a negative or original record of the type shown in Fig. 4. The double copying, as well as the use of formers, may then be' dispensedwith and positive 7 or reproduction copies may be made by the usual photographic processes.

What is claimed is:

l. The method of making sound films which includes, first, the step of making a negative photographic record of sound on a sensitized film strip by varying widths of exposure of the film in accordance with sound, second, the step of'making a positive film copy of said negative record, and third, the step of exposing the portionsoi the positive film not used for the sound record which consists in exposing the unused portion up to a line adjacent to, and parallel with, a line drawn through the general apices of the unexposed por-. tions representing sound.

2. The method of making a photographic sound film for optical reproduction which consists in recording sound on a sensitized film strip in ac cordance with-sound and shuttering the exposedportions up to a line adjacent to and parallel with a line drawn through the general apices of the unexposed portions representing sound, developing such film to obtain a negative, and afterwards copying this negative film on a positive film.

3. A sound film for optical reproduction in which the width of the exposed portion varies in accordance with sound, the transparent portions of the film being opaque up to a line ad- Jacent to and parallel with a line drawn through the general, apices of the exposed portions representing sound. 1

4. A sound film for electro-optical reproduc-' tio'n, successive portions of which film vary in their permeability to light in accordance with the intensity of the sounds, the means permeability to light being smaller "at portions corresponding to sounds oil-relatively small intensity than at portions corresponding to sounds of relatively great intensity.

5. The method of producing a modified photographic sound record from an original photographic sound record, that includes producing a photographic opaque modification band of varying width by reference to the amplitude characteristics of the ori inal record, and combining on a. film in proper register with each other said varying width modification band and a print of saidori'ginalrecord.

6. The method of producing a modified photographic sound record from. an original photographic sound record, that includes producing a photographic opaque modification band of varying width by reference to the amplitude characteristics of the original record, and combining on a film in proper register with each other a print of said v'aryingwidth modification band and a print of said original record.

7. The method of producing photographic sound records, that includes producing a normaloriginal photographic sound record,'producing a photographic varying width band of opacity whose width is correlated in required manner with amplification characteristics found in the original record, and combining on a film in proper \register with each other said varying width band and an original record. I

8. The method of producing a shadingrecord upon a photographic film having a sound record thereon, said shading record being incapable of reproducing sound, which consists in subjecting a separate portion of the film to a source of light and varying the degree to which said portion of the film is subjected to said light by exposing more or less of the film in accordance with the variations in amplitude of the sounds.

9. The method of photographically producing a shading record, said record being distinct from the sound record itself and incapable of reproducing sound. which consists in subjecting a film to a source of light and varying the extent to which said film is subjected to said light by exposing more or less of the film to said light accordingly as the sounds are increased or diminished in amplitude.

10. The method of photographically producing a shading record. as distinguished from a sound record, upon a film which consists in causing a portion of the film to traverse the rays emanating from a source of light, and in increasing or decreasing the exposed width of said portion of the film to produce exposures varying as the sounds are increased or diminished in amplitude or power.

11. The method of producing a shading record, said record being distinct from the sound record and incapable of reproducing sound, which consists in exposing more or less of a photographic film to a constant source of light simultaneously as the sounds are being recorded whereby to produce varying areas of exposed film surface, said varying areas being in correspondence with the variations in amplitude or power of the sounds recorded.

12. The method of controlling the volume of noise reproduced from a photographically recorded sound record which comprises progressively obscuring the normally clear portions of the sound-track area whereby to control the amount of light passing through said soundtrack and thereby to control the volume of noise reproduced. v

13. The method of producing a sound record which comprises recording the sound upon a photographic sound-track, and recording the volume of said sound independently upon the same record track.

14. The method of producing a sound record comprising a single photographic sound-track which comprises recording the sound upon the record and recording the average volume'of said sound independently upon the same record track.

15. The method of recording sound which comprises producing a variable area record of the sound being recorded and varying the width of said variable area record in accordance with the average volume of said sound.

18. The method of recording sound which comprises producing a sound-track including a variable area record of the sound being recorded and varying the area of the clear portions of said sound-track in accordance with the average volume of said sound.

17. The method of making photographic sound records adapted to produce a minimum amount of ground noise upon reproduction which comprises exposing a sensitive film to a light beam, varying one side of said light beam in accordance with the wave form of the sound being recorded and varying the other side of said beam in accordance with a component of said wave.

18. The method of making variable width photographic sound records, in which the clear area varies in accordance with the volume of the sound being recorded, which comprises, exposing a sensitive film to a single light beam, vibrating one edge of the beam laterally of the film in accordance with the sound wave being recorded and simultaneously producing a lateral displacement of the other edge of the beam in accordance with a component of said wave.

19. A sound record comprising regions of darkness interspaced with regions of lesser darkness characterized in that the average-darkening of the background regions varies in accordance with the average intensity of the sound recorded.

20. A photographic record of sound comprising regions of darkness interspaced with regions of lesser darkness characterized in that the area of darkening of the background regions varies in accordance with the average volume of the sound recorded.

21. A photographic record of sound comprising regions of darkness interspaced with regions of lesser darkness characterized in that one boundary of said regions of lesser darkness varies in accordance with a sound wave and another boundary of said regions varies in accordance with a component of said wave.

22. In combination, means for exposing a light sensitive surfaceta light, means for causing said light to vary in response to sound. and additional means for causing the amount of said light reaching said surface to vary, said additional means being independent of said first mentioned means.

23. In combination, means for exposing a light sensitive surface to light, means for causing said light to vary in response to sound, and independent additional means for causing the average amount .of said light reaching said'surface to vary as a function of the loudness of the sound being recorded.

.24. In combination. means adapted to continuously expose a light sensitive surface to the action of a beam of light, sound controlled means for influencing said light, and independent additional means controlled by the loudness of the sound for further influencing said light.

. 25. Apparatus for recording sound on a moving light sensitive member, comprising means for variably exposing the member in accordance with sound waves, and means for varying said exposure in accordance with the amplitudes of said sound waves independently of their frequencies.

28. Apparatus for recording sound on a moving light sensitive member, comprising means for variably exposing the member in accordance with sound waves; and means for simultaneously varying said exposure in accordance with the amplitude of said sound waves independently of their frequencies. I

27. In combination, means for making a photographic sound record within a single sound-track area, and means controlled by the audio current of the sound being recorded for continuously altering the character of the record so that, when the original sounds are reproduced therefrom, ground noise is minimized, said means including means responsive to said current for shading the normally clear portion of the finished soundtrack area to the maximum amount possible to still permit obtaining suflficient clear portion to properly reproduce the recorded sound.

28. In combination, means for making a photosive to saidcurrent for shading the normally,

clear portion of said sound-track area to the limit possible still retaining sufiicient of saidclear portion to permit accurate reproduction of recorded sounds.

29. In combination, means for exposing alight sensitive surface to light, means responsive to. audio, current impulses for causing said light to vary in response to sound, and additional means controlled by said impulses for causing the amount of light reaching said surface to vary independentlyof the frequencies recorded by said first mentioned means.

30. In combination, means for exposing a light sensitive surface to light, means responsive to said audio current impulses for causing said light to vary in response to sound, and independent additional means controlled by said impulses for causing the average amount of light reaching said surface to vary as a function of only the loudness of the sound being recorded.

31. In combination, means responsive to audio current impulses for directing a narrow line of light into a portion of film reserved for photographic sound record, means for causing one end of said line'to move transversely of said film in response to sounds, and means controlled by said impulses for causing the other end of said line to assume and maintain an average position with respect to the boundary of said portion corresponding to the loudness of the sound represented by said record.

32. The method of making a sound track on a moving sensitive film, which comprises transmitting a beam of light to the film and separately varying in accordance with waves of different character, the position of the two edges of the light beam corresponding respectively with the two edges of the sound track.

33. The method of recording sound on a moving sensitive film which comprises producing a line of light on'the film transversely to the direction of movement of the film, varying thelength of the line at one end in accordance with a characteristic of sound, and varying the length of the line at the other end in accordance with another characteristic.

34. In apparatus for use in recording sound on a moving photographically sensitive -film, means for transmitting a beam of light to the film for tracing a record track thereon, means for varying the position of one edge of the track in accordance with sound wave energy of certain character, and means for varying the position of the other edge of the track selectively in accordance with wave energy of different character.

35. In a light controller for use in conjunction with a line source of light in recording sound on a moving sensitive film, a vibratable light modulator and means to vibrate the same to vary the length of the line at one end of the line in accordance with sound controlled current, and another vibratable light modulator and means to vibrate the same to vary the length of said line at the other end selectively in accordance with a current having a characteristic differing from that of said first mentioned current.

36. In a light controller for use in recording sound on a moving sensitive film; means arranged to-define the length of a line of light to be produced on the film, said means including means to vary the length of the line-at one end in ac-' cordance with sound controlled current and means to vary the length of the line at the other end selectively in accordance with a current having a characteristic diflering from that of said first mentioned current.

37. In apparatus for use inrecording sound on a moving sensitive film, means for producing a line of light on the film transversely to the direction of movement of the film, means to vary the-length of the line at one end in accordance with sound controlled current, and means to vary the length of the line at the other end selectively in accordance with a current having a characteristic diflering from that of said first mentioned current.

38. In apparatus for use in recording sound on a moving photographica-lly sensitive film, means for transmitting a beam of light to the film for tracing a record track thereon, means for varying the position of one edge of the track in accordance with sound wave energy of certain frequency, and means for varying the position of the other edge of the track selectively in accordance with wave energy of diiferent frequency.

39. In apparatus for use in recording'sound on a moving sensitive film, means for defining the length of a lineof light to be produced on the film transverselyfothe direction of movement of the film, said means including means to vary the length of the line at one endin accordance with sound controlled current within a certain frequency range and means to vary the length of the line at the other end selectively in accordance of the sound track selectively in accordance with high frequency components of a sound wave, and vibrating another edge of the light beam corresponding with the other edge of the sound track selectively in accordance with low frequency components of a sound wave.

41. In apparatus for use in recording sound on a moving sensitive film, means for defining the length of a line of light to be produced on the film transversely to the direction of movement of the film, said means including means to vary the length of the line at one end selectively in accordance with high frequency current and means to vary the length of the line at the other end in accordance with low frequency current.

42. In apparatus for use in making a variable width sound record on a moving sensitive film, means for defining the length of a line of light to .be produced on the film transversely of the direction of movement of the film, said means -including a vibratable light modulator for varying the length of the line at one end of the line and another vibratable light modulator for varying the length of the line at the other end of vibrating the other of said modulators.

43. In apparatus for making a' negative photographic sound film the positive copy or which is. intended to be reproduced optically. means for recording the sound by varying width of the ex- .posed portion of the film in accordance with sound, an auxiliary shutter arrangedin the path or the light, and an electrical system for varying the aperture of the shutter in such a manner that the usually exposed part oi the film remains covered and unexposed up to a line adjacent to and parallel with a llnedrawn through the general apices oi the unexposed portions representing sound.

44. In an apparatus jor making a negative photographic sound film the positive copy of which is intended to be reproduced optically, means for recording the sound by varying width or the exposed portion of the film in accordance with sound, an auxiliary shutter in the optical path or the apparatus, having an aperture which is variable in the transverse direction or the him, a microphone, and a reiector circuit through which the currents of said microphone flow to control said shutter electromagnetically in such a manner that the usudlly exposed part 01 the film remains covered and unexposed up to a line I adjacent to and parallel with a line drawn through the general apices oi the unexposed portions representing sound.

45. A photographic record of sound comprising regions ot darkness varying, with the sound,

and regions of darkness shading the normally 4 lighter portions or the record to the maximum amount possible to still permit properly reproducing the sound.

46. The method of reducing the noise.reproduoed irom a photographicaiiy recorded sound recordwhioh comprises progressively obscuring the sound track inversely with the volume 01 sound recorded.

47. The memos-er recording sound which coinprises moving a sensitive medium at constant speed through a beam of Kent. varying said beam in accordance with the instantaneous variations in the sound to be recorded, and varying the average power oi said beam directiy'with the volume 01 the sound.

48. The method or recording sound which comprises producing electrical waves varying inac cordance with the sound, utilizing a portion of said waves for controlling the production of an impression in a photographic medium varying in accordance with said waves and simultaneously utilizing another portion oi said waves for modibeam so that in the absence oi sound the quantity of light energy impressed upon said medium is small, increasing the average quantity oi light energy impressed upon said medium with an increase in" the amplitude oi the soundwaves recorded, and varying the quantity oi light energy impressed upon said medium in accordance with the instantaneous variations in the sound recorded.

ERWIN GERLACH.

- CERTIFICATE or qomcrron. Y I Patent no. 2,206,5h7. w July 2', 19140.-

' mun smog.

It '15 hereby oertifledjhafi error eppeare 1;; the printed s ecificat on of the above numbered. patent reqoiring correction as follows: Page 5, second oolumn, line 1 strike out the article '"a" before "microphone" first. ocourrehce; li le 1+8, olaim 1+, for "moans" reed --mean--;.and that the sold Letters Retent should. be read Withithis correction therein that the same maroo nrom to the recbrdor the case in thefiPte'nt 031.co-

Signed and. sealed this let a; or October, A. D. 19MJ Henry Van Areda1e,' I (BQll)- Acting Comieeioner -01 Patents. 

